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Science and Astronomy Questions

Science and Astronomy Questions

Posted: 22 Apr 2017 06:13

by A-L-E-X

Watsisname wrote:

Hornblower, The origin of the highest energy cosmic rays, and why we observe as many as we do despite the expectation that the CMB would apply an important breaking effect to them, is a significant unresolved problem in astrophysics. Dark energy is also pretty darn mysterious, but I'm doubtful that there is any important connection between the two.

When modeled as a cosmological constant, dark energy is a type of gravitational field (more generally, a correction to the metric of space-time) and so it affects all particles equivalently.

Dark energy also can't accelerate particles in a particular direction. Intuitively one would think dark energy would expand the universe by "pushing out" on things, but that's actually not how it works -- in cosmology it can't work that way because there is no preferred direction to push from and no walls to push against. The dark energy is uniform and so it does not apply a net force on anything. Instead, it affects the expansion of space itself because of its energy density, which changes the metric of space-time.

Didn't we observe some off-the-charts cosmic ray particle a few years ago that had the energy of a fast ball (pretty amazing for a subatomic particle.) It had extragalactic origins.

Science and Astronomy Questions

Posted: 22 Apr 2017 06:21

by A-L-E-X

Watsisname wrote:

A-L-E-X wrote:

Source of the post I was thinking of using both a UV403 filter and an IR720 filter to filter out visible light and see if I can detect the "invisible" parts of the rainbow with the camera. Not sure if it's possible because cameras have blocking filters on them. I can do IR photography- but the camera's blocking filter removes about 8 stops of IR light, and on the other end of the spectrum, about 13 stops of UV light.

Yeah, that's a pretty big reduction, but I guess that means the filters are doing their intended job. There are some guides online for how to modify the camera with taking the filters out, but it's probably not something you want to try unless you are really serious about it and have equipment to spare. If you're managing to get some results with the filter in place then that's pretty awesome. I really enjoy looking at B&W infrared photography -- it gives an amazing way to see the world and can produce some really interesting art. People's faces in particular are very strange in IR, and landscapes and foliage are neat too.

I'd love to see some shots you have made!

A-L-E-X wrote:

Source of the post Some of the amazing things I found out is that although most of us humans have three types of cones to detect color (thus three primary colors), some lucky people have a fourth type of cone (four primary colors!) so they can actually see more color than normal people can? And who said that superhumans didn't exist

I've heard of this and it does sound pretty interesting. And there are other superhuman senses as well. I had the privilege to meet a "supertaster" who puts that skill to use as the blendmaster of a tea company. People also generally have a broader range of hearing when they are young, and lose the sensitivity to high frequencies as they age. I used to be very sensitive to higher frequencies than normal, and have a vivid memory of walking through a neighbors yard with some friends and was suddenly incapacitated by a soul-piercing sound that nobody else could hear. Turns out we had walked in front of a motion-sensitive deer deterrent that throws out ultrasound.

This gets more into the realm of neuroscience than color theory, but have you ever heard of a condition called hemineglect? I think it's one of the weirdest things about how people can perceive the world differently.

The photosynthesis of plants really stands out in IR and I feel like you can see a bit under the skin with it also, which is why it creates those haunting portraits. I've also done false-color images in IR, you must take care to keep the WB at its lowest possible temperature- I keep it at 2000K- otherwise the picture becomes overwhelmed with red (and with blue when you flip color channels.)Wow, the supersensing thing is intriguing! I've heard that as young children we can see many more stars (and even the Galilean moons of Jupiter!) and some children even report being able to see the moon move across the sky. As we get older our vision deteriorates. Although some sharp sighted adult viewers have reported being able to see stars all the way down to Mag 8.5 from high altitude/low light pollution locations.Hemineglect? Never heard of it- but just breaking down the term, does it have to do with some senses atrophying because we don't use them as much when we get older? Just a shot in the dark lol.

Science and Astronomy Questions

Posted: 22 Apr 2017 06:24

by A-L-E-X

Watsisname wrote:

Hornblower, The origin of the highest energy cosmic rays, and why we observe as many as we do despite the expectation that the CMB would apply an important breaking effect to them, is a significant unresolved problem in astrophysics. Dark energy is also pretty darn mysterious, but I'm doubtful that there is any important connection between the two.

When modeled as a cosmological constant, dark energy is a type of gravitational field (more generally, a correction to the metric of space-time) and so it affects all particles equivalently.

Dark energy also can't accelerate particles in a particular direction. Intuitively one would think dark energy would expand the universe by "pushing out" on things, but that's actually not how it works -- in cosmology it can't work that way because there is no preferred direction to push from and no walls to push against. The dark energy is uniform and so it does not apply a net force on anything. Instead, it affects the expansion of space itself because of its energy density, which changes the metric of space-time.

This is all very interesting- the three "darks" I wonder about are dark energy, dark matter and dark flow. There is also the "Great Attractor" and why do superstructures in the universe resemble the structure of neural networks of our own brains? Maybe on a fractal level there is an equivalency (just on different scales) because they are both quantum computers.

Science and Astronomy Questions

He describes it as a bubble of space-time geometry which carries its contents backward and forward through space and time as it tours a large circular path. The bubble moves through space-time at speeds greater than the speed of light at times, allowing it to move backward in time.

Science and Astronomy Questions

Posted: 29 Apr 2017 03:15

by Watsisname

A-L-E-X wrote:

Source of the post Hemineglect? Never heard of it- but just breaking down the term, does it have to do with some senses atrophying because we don't use them as much when we get older? Just a shot in the dark lol.

No, it's way weirder, and usually is a result of damage to the brain. A person with hemineglect "neglects" half of space. Not because they cannot see it (their eyes work just fine), but because their brain is unable to process or even contemplate it. For example, you might ask a person with this condition to draw a clock, and they will cram the numbers all on one side, neglecting the other half. It's as if the other half of the clock does not exist.

A-L-E-X wrote:

Source of the post There is also the "Great Attractor" and why do superstructures in the universe resemble the structure of neural networks of our own brains?

A funny coincidence. The structure that evolution developed which optimizes the storage and transmission of information in brains happens to look similar to the 3D structure formed by gravitational collapse of a fluid with small initial density fluctuations. We can model the formation of the cosmic web this way using just gravitational forces in the Lambda-CDM model and it reproduces the observed structure amazingly well.

Cute! Essentially identical to doing this, but with math and general relativistic rigor.

Science and Astronomy Questions

Posted: 29 Apr 2017 05:00

by Hornblower

I have been trying to figure out a simple math question for a while now. Maybe someone can help. I'm trying to figure out an equation of a u shape where the cusp makes a perfect half-circle. (Not a parabola). I made a graph on Desmos to show you what I mean.

Science and Astronomy Questions

Posted: 29 Apr 2017 05:13

by Watsisname

I think it would have to be defined piece-wise, because the derivatives (slopes) are not continuous -- they change discontinuously when you go from the half-circle part to the straighter and more vertical sides. The half-circle part can be described by y=-sqrt(r^2 - x^2) + r, where r is the radius of the half-circle. And if the sides are truly vertical, use x= +/- r. Then the combination is:

y = -sqrt(r^2 - x^2) + r, with x from -r to r,x = +/- r, with y>r

There might also be some linear combination of even functions (like x^2, x^4, x^6...) that approach what you want. I'm not sure.

Science and Astronomy Questions

Posted: 29 Apr 2017 05:32

by Hornblower

yeah. That's how I made that graph, with peace-wise functions. I was looking for a single function that described it.

Science and Astronomy Questions

Posted: 29 Apr 2017 06:21

by Watsisname

Ah, I see. And I found that there is in fact a linear combination of functions that will work:

The series expansion x^2/2 + x^4/4 + x^6/8 + x^8/16 + ... will approximate the curvature of the circle. And the function x^(very large even number) is virtually flat between -1 and 1 but very steep outside, so if you add them together they will approach the shape you want in a single analytical function. For example,

y = x^2/2 + x^4/8 + x^6/16 + x^8/32 + x^10/64 + x^100

Science and Astronomy Questions

Posted: 29 Apr 2017 07:09

by Hornblower

Awesome! Thanks

Science and Astronomy Questions

Posted: 30 Apr 2017 00:07

by Watsisname

Of course!

Going back to hemineglect: here are a couple good videos about it with some interviews of patients with the syndrome. The demonstration where the interviewer asks which finger he moves is remarkable. It is not as simple as a problem of vision, it's a problem of how the mind thinks about space.

The implications of this are very interesting: you do not see the world. You see a model of the world that your mind constructs, which, if constructed well, happens to be consistent with the world in order to allow you to understand and interact with it.

Science and Astronomy Questions

Posted: 30 Apr 2017 02:18

by Voekoevaka

Watsisname wrote:

Ah, I see. And I found that there is in fact a linear combination of functions that will work:

The series expansion x^2/2 + x^4/4 + x^6/8 + x^8/16 + ... will approximate the curvature of the circle. And the function x^(very large even number) is virtually flat between -1 and 1 but very steep outside, so if you add them together they will approach the shape you want in a single analytical function. For example,

y = x^2/2 + x^4/8 + x^6/16 + x^8/32 + x^10/64 + x^100

This is nos exactly the right series for it. At x=0, the series expansions will be : x2/2 + x4/8 + x6/16 + 5x8/128 + …This will approximate only the shape of the circle, and it can't include the two half-lines beside, as the union of all is not an analytic curve. So if you want to get all the curve with a single equation, you should use non-analytic functions such as :sqrt(1-min(0,(y-1))^2) = abs(x)

Science and Astronomy Questions

Posted: 30 Apr 2017 03:29

by Watsisname

Goes to show I shouldn't do math when tired -- interpreted the pattern of the expansion wrong and couldn't even copy it right either. Thanks for correcting! I think it's still valid though that for the series approximation, adding x^(2n) to it (for very large n) will also approximate the straight sides without severely changing the semicircle's curvature.

This weakness of this approach is that it takes a lot of terms to approximate out to the sides of the semicircle, but even just going up to x6/16 and adding x100 isn't bad.

Science and Astronomy Questions

Posted: 07 May 2017 17:03

by A-L-E-X

Watsisname wrote:

A-L-E-X wrote:

Source of the post Hemineglect? Never heard of it- but just breaking down the term, does it have to do with some senses atrophying because we don't use them as much when we get older? Just a shot in the dark lol.

No, it's way weirder, and usually is a result of damage to the brain. A person with hemineglect "neglects" half of space. Not because they cannot see it (their eyes work just fine), but because their brain is unable to process or even contemplate it. For example, you might ask a person with this condition to draw a clock, and they will cram the numbers all on one side, neglecting the other half. It's as if the other half of the clock does not exist.

A-L-E-X wrote:

Source of the post There is also the "Great Attractor" and why do superstructures in the universe resemble the structure of neural networks of our own brains?

A funny coincidence. The structure that evolution developed which optimizes the storage and transmission of information in brains happens to look similar to the 3D structure formed by gravitational collapse of a fluid with small initial density fluctuations. We can model the formation of the cosmic web this way using just gravitational forces in the Lambda-CDM model and it reproduces the observed structure amazingly well.